[Cluster-devel] [GFS2 PATCH] gfs2: fix use-after-free in trans_drain

[Bob Peterson <rpeterso@redhat.com>]

This patch adds code to function trans_drain to remove drained
bd elements from the ail lists, if queued, before freeing the bd.
If we don't remove the bd from the ail, function ail_drain will
try to reference the bd after it has been freed by trans_drain.

Thanks to Andy Price for his analysis of the problem.

Reported-by: Andy Price <anprice@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
---
 fs/gfs2/log.c   | 4 ++++
 fs/gfs2/trans.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 16937ebb2a3e..760af666576c 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -998,12 +998,16 @@ static void trans_drain(struct gfs2_trans *tr)
 	while (!list_empty(head)) {
 		bd = list_first_entry(head, struct gfs2_bufdata, bd_list);
 		list_del_init(&bd->bd_list);
+		if (!list_empty(&bd->bd_ail_st_list))
+			gfs2_remove_from_ail(bd);
 		kmem_cache_free(gfs2_bufdata_cachep, bd);
 	}
 	head = &tr->tr_databuf;
 	while (!list_empty(head)) {
 		bd = list_first_entry(head, struct gfs2_bufdata, bd_list);
 		list_del_init(&bd->bd_list);
+		if (!list_empty(&bd->bd_ail_st_list))
+			gfs2_remove_from_ail(bd);
 		kmem_cache_free(gfs2_bufdata_cachep, bd);
 	}
 }
diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
index ab96cf0bf26b..63fec11ef2ce 100644
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -169,6 +169,8 @@ static struct gfs2_bufdata *gfs2_alloc_bufdata(struct gfs2_glock *gl,
 	bd->bd_bh = bh;
 	bd->bd_gl = gl;
 	INIT_LIST_HEAD(&bd->bd_list);
+	INIT_LIST_HEAD(&bd->bd_ail_st_list);
+	INIT_LIST_HEAD(&bd->bd_ail_gl_list);
 	bh->b_private = bd;
 	return bd;
 }